The explosive rise in popularity of smart phones has drastically increased the demand for ubiquitous mobile data services. To cope with the exponential growth in mobile data traffic, it is anticipated that new radio spectra with substantially larger bandwidths than those available today for mobile communications will be needed in the future. As a result, technologies that enable wireless communications over high-frequency bands (e.g., millimeter wave (mmW) bands) where large amounts of under-utilized spectrum are available have recently received much attention.
Communicating wirelessly over high frequency bands, such as the mmW bands, are not without challenges. Radio signals transmitted over such bands typically suffer from higher path loss than those transmitted over the lower frequency bands that are currently used in cellular communications. The problem is further exacerbated in the unlicensed 60 Gigahertz (GHz) band where radio signals suffer additional losses due to oxygen and rain absorption.
In order to overcome the resulting tight link budget, wireless communications over high frequency bands have to rely on a large directional gain achieved by forming narrow beams of radio signals using, for example, an adaptively steerable antenna array. Fortunately, the shortened wavelengths in high frequency bands make it possible for a device, such as an Access Node (AN) or User Equipment (UE), of reasonable size to be equipped with a relatively large number of antennas for narrow beamforming. A large number of antennas provide a communication device with access to high spatial resolution. However, high spatial resolution also induces high spatial uncertainty. Due to the high spatial selectivity resulting from narrow beamforming, a slight error in the choice of beam direction can lead to drastic decrease in Signal-to-Noise Ratio (SNR). As such, there is a need for an effective beam finding procedure in order for a wireless communication device (e.g., an AN or a UE) to identify the proper beam direction to communicate with its partner.